Revised by Nelson and Goldman (1934a) and Russell (1968a, b), who included Cratogeomys as a valid subgenus of Pappogeomys, a position followed by Hall (1981) and Patton (1993). However, Honeycutt and Williams (1982), based on a phylogenetic analysis of allozyme data, and DeWalt et al. (1993a) and Demastes et al. (2002), using mitochondrial DNA sequences, confirmed Russell’s hypothesis of the sister relationship between Pappogeomys and Cratogeomys, but treated the two as separate genera. While it remains a matter of personal opinion as to the distinction between genera and subgenera, I choose here to follow the current consensus of workers on this group (e.g., Lee and Baker, 1987; Davidow-Henry et al., 1989; Hollander, 1990). Russell (1968b) recognized two species groups, the castanops group (with castanops and merriami) and the gymnurus group (with fumosus, gymnurus, neglectus, tylorhinus, and zinseri). While these groups have been confirmed by molecular phylogenetic studies (e.g., DeWalt et al., 1993a; Demastes et al., 2002), both studies call into question the species boundaries recognized by Russell and earlier workers. Some changes are incorporated into the accounts below, but additional ones are likely following the completion of on-going studies by M. S. Hafner, J. W. Demastes, and co-workers (pers. Comm.). Hooper (1946) included Platygeomys within Cratogeomys. This name, with gymnurus as its type species, would be available for Russell’s gymnurus group, should that group warrant formal recognition. Key to eight species listed below given in León et al. (2001, Mammalian Species No. 685).